120 PLANAEIA. 



Its history in the Treatise on Planaria in 1814, left numerous in- 

 teresting questions unnoticed, therefore, in the hopes of verifying facts, and 

 of correcting errors, a rigorous search was not only renewed in the very 

 place where they were formerly not difficult to be taken, but extended 

 over the neighbouring districts for several years, yet not a single speci- 

 men could be discovered. 



A favourable opportunity at length conducted me to the original 

 sites of these animals in the year 1822. My search was resumed, and 

 it proved successful. I collected fifty with great facility on the 8th of 

 May. 



However, some other animals, sufficiently numerous in the same 

 place on former occasions, did not now appear, either having been extir- 

 pated, or from still lurking in their retreats, as the weather was chill. 

 There are conditions, yet mysterious to mankind, regulating the preser- 

 vation and multiplication of animated beings. They cease to exist in 

 particular places for a time without absolute extirpation from the district. 

 Their numbers may be so reduced that they escape farther observation. 



All the preceding Planarise were of a beautiful grass-green ; they 

 seemed nearly of equal size ; and almost the whole contained ova grouped 

 in every possible arrangement. At least ten or twelve could be enume- 

 rated in several ; sometimes in the right, sometimes in the left of the 

 body : one or two were advanced a little before the rest. Their position 

 was so much diversified, that it was never alike in any two specimens. 



From May 17, shining corpuscula, together with what seemed de- 

 caying animal fragments, appeared in the vessels containing the captive 

 animals. The former proved so many ova liberated on decomposition 

 of the Planariae, numbers perishing daily from the great heat of the 

 season, which suddenly changed. Such was the mortality, that not one 

 Planaria remained in a week. 



These creatures are very prolific, forty ova lay in a vessel which had 

 contained only three. 



About 100 ova were now transferred to a place deemed suitable for 

 exclusion of the young. But none came forth. 



Greater inequality, than previously, prevailed among a second colony 



